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Optoelectronics such as Si avalanche photodiodes (APDs) used in space are subjected to background cosmic radiation including highly energetic heavy ions. As these swift ions pass through a device, they lose energy by promoting free electron-hole pairs. The resultant ionization track is an extremely dense two-component free carrier plasma with submicron radial diameters. Within the track, injected space charge is high enough to severely distort the local electric field, which perturbs the current transient or impulse response induced on the device electrodes. In this paper, the time-resolved ion beam induced current response of a low breakdown bias, high-frequency Si APD has been observed for a sequence of front side irradiations with MeV heavy ions species with different track geometries. These results are compared with focused picosecond laser experiments, where injection levels are controlled from low to high. Ion induced tracks are found to effectively quench the avalanche process. Simulations using Synopsis technology computer aided design are performed to clarify the role of screening in quenching avalanche mechanisms under the conditions prevalent here. [ABSTRACT FROM AUTHOR]

The generation of single event transients generated by the impact of high-energy ions in high-speed photodetectors leads to bit error rate degradation in optical communications in radiation hard environments such as space. High-energy heavy ions, in particular, generate a submicron electron-hole pair plasma with a picosecond temporal profile that results in ultrahigh-injection carrier dynamics which induce large space-charge effects. These space-charge effects disturb the local electric field, thereby determining the peak and duration of a single event transient. In this paper, we examine the transient response of Si p-i-n photodetectors irradiated with focused single MeV heavy ions for a range of ion energies chosen to ensure the same end of range but different average plasma densities. We discuss the role of high-injection effects on the evolving spatiotemporal response with the aid of three-dimensional technology computer-aided design software. The result of both measurement and simulation points to charge collection being dominated by three clearly separable phases: (a) an ultrafast bandwidth-limited response which follows the excitation function, (b) an ambipolar diffusion-dominated expansion phase where space-charge screening limits the extracted current, and (c) a bipolar phase where the external field penetrates the electron-hole pair plasma resulting in rapid collection by drift. [ABSTRACT FROM AUTHOR]